PICRIC ACID Ig PREPARATION 80. Picric Acid (Trinitrophenol), C0H9(OH)^No! 4 1 ' XN02 6 Woulfe, 1771 ; Schmidt, Glutz, Bcr^ 1869, 2, 52. * I * I 25 grms. phenol. l|^ 25 „ cone, sulphuric acid. \'fl i QQ „ (70 c.c.) cone, nitric acid, sp. gr. 1*4. - j* 25 „ (20 c.c.) fuming nitric acid, sp. gr. 1-5. |' tf<) The phenol and concentrated sulphuric acid are heated ,<' i together in a ])orcclain basin for a few minutes, until a clear V* solution of phenol sulphonic acid is obtained. It is diluted. '* with half its volume of water, well cooled, and then slowly 4 added, in small quantities at a time, from a tap-funnel, to the ^ nitric acid contained in a flask (r litre), and well shaken.*- \f The liquid assumes a, deep red colour, a considerable rise of If temperature occurs, and red fumes are evolved. When the -f* phenol sulphonic acid has been added, the flask is placed on. *d the water-bath and heated, with the addition of 25 grams fuming- nitric acid, for i.....2 hours.* On cooling, picric acid separates out as a yellow, crystalline mass. It is diluted with water, filtered at the pump, and washed free from the mother liquor with cold water. It is then purified by recrystallisation from a large quantity of hot water acidified with a few drops of sulphuric acid. Yield, about 30 grains. CJ l,(011) +1 F,SO., - C0H4(0H).S03H + H20. C(;Ha(OH)(NOa)3 + 3H20 + H2SO4. if ft Properties.-—Yellow, prismatic crystals; m. p. 122*5°; sub- ^i limes on gently heating ; explodes on detonation ; easily soluble \\\ alcohol and ether ; with difficulty in cold, more readily in f| hot water ; the solution has a bitter taste. Reactions.— r. To an aqueous solution of picric acid add a little potassium cyanide solution, and warm. A brown crystal- line precipitate of isopurpuric acid separates. 2. Add picric acid and a few drops of caustic socla to a dilute solution of grape sugar, and warm. The liquid turns deep brown.